An example of a suitable host processor is the IBM (International Business Machines Corporation) Series/1 processor, and an example of a suitable I/O controller is an IBM Type 4966 I/O controller, which is particularly adapted for use with the Series/1 processor. An example of a system such as that shown in FIG. 1 is described in more detail in commonly assigned U.S. Pat. No. 4,426,637 to Brown et al.
FIG. 1 is a block diagram showing a data processing installation where the present invention can be used to advantage. The system includes a host processor 10 composed of a main storage unit 11, a central processing unit (CPU) 12 and a console 13. The I/O controller 20 is provided to interface the host processor 10 with an I/O device 30. The I/O controller 20 includes interface circuits 21 which connect the I/O controller channel 15 from the host processor 10 to the I/O device 30, a microprocessor 22 which controls the operations of the interface circuits 21, and two memories which the microprocessor 22 requires for performing its control operations. The two memories are a read-only storage (ROS) 23 and a random access memory (RAM) 24, both of which are communicated with the microprocessor 22 via a bus 25.
It is often required to test the functioning of the I/O controller and the I/O device 30, either to verify their operation during the manufacture of the system or to diagnose problems in the field. To carry out such testing, it is desired to be able to examine the contents of the ROS 23 and RAM 24, to alter the contents of the RAM, and to display designated segments of data, particularly, data communicated from the I/O device 30. In the prior art, it has been the practice to connect to the I/O controller via the I/O channel 15 a separate test device which is called an "I/O attachment console". An example of such an arrangement is described in commonly assigned U.S. Pat. No. 4,268,902 to Berglund et al.
Although test installations such as that described in the Berglund et al. patent were capable of testing the desired functions of the I/O controller, nevertheless, they were disadvantageous for several reasons. First, it was time consuming to set up the test installation in that the covers of various system units had to be removed and cables disconnected and reconnected through the test device. The operations of the entire data processing system had to be shut down while this was taking place. Moreover, the presence of the test device itself could contribute to the problem being diagnosed, for instance, if the problem were due to electromagnetic interference. This made it very difficult to pinpoint the source of a problem in many instances.
IBM Technical Disclosure Bulletin, Vol. 19, No. 10, March 1977, authored by D. C. Solly, describes debugging user programs for use with a "console-less" controller. Although such programs could allow for some testing of the I/O controller without the need for an I/O attachment console, they are not fully acceptable in many situations due to the fact that the user's software program had to be modified greatly to accommodate the debugging programs.
Overcoming these disadvantages, the present invention provides a method for testing predetermined functions of an I/O controller in which it is not necessary to greatly disturb the ordinary processing operations of the data processing system of which the I/O controller to be tested forms a part. Particularly, the invention provides such a method in which it is not necessary to disconnect any of the cables of the data processing system and to connect in an I/O attachment console.
Further, the present invention provides such a method for testing an I/O controller in which it is not necessary to modify any of the user's software, and wherein the data processing system can continue its ordinary data processing operations after the testing of the I/O controller has been carried out.